Meiosis notes

Copy the questions & use 10.1 Copy the questions & use 10.1 p. 270 to answer them.p. 270 to answer them.

1.1. What are chromosomes made of?What are chromosomes made of?2.2. What is a gene?What is a gene?3.3. Draw a pair of homologous Draw a pair of homologous

chromosomes.chromosomes.Answer these after we finish taking Answer these after we finish taking

notes:notes:4.4. Compute the number of chromosomes Compute the number of chromosomes

that the gametes of a cat (2n=38 that the gametes of a cat (2n=38 chromosomes) will have. Show work.chromosomes) will have. Show work.

5.5. Compare/contrast Telophase I and II.Compare/contrast Telophase I and II.

Chromosomes and Chromosome Number

Human body cells have 46 chromosomes

Each parent contributes 23 chromosomes

Homologous chromosome -one of two paired chromosomes, one from each parent

Homologous ChromosomesHomologous Chromosomes Same length Same centromere position Carry genes that control the same

inherited traits One came from Dad, &One came from Dad, &

one came from Mom!one came from Mom!

An organism produces gametes to maintain the same number of chromosomes from generation to generation.

Compare diploid and haploid Compare diploid and haploid numbernumber

Diploid: cell that Diploid: cell that contains two of each contains two of each kind of chromosome (2N)kind of chromosome (2N)

Body cells(somatic cells) Body cells(somatic cells) are diploidare diploid

Haploid: cell with only Haploid: cell with only one kind of chromosome one kind of chromosome (N) (N)

Gametes (sex cells) are Gametes (sex cells) are haploidhaploid

Meiosis I

The sexual life cycle in animals involves meiosis.

Meiosis produces gametes. When gametes combine in fertilization, the number of chromosomes is restored.

Meiosis IProphase I each chromosome pairs with its

corresponding homologous chromosome to form a tetrad(4 chromatids)

The nuclear envelope breaks down. Spindles form.

**Crossing-over- chromosomes will switch some genes. (genetic variation)

Crossing OverCrossing Over

Metaphase I Homologous pairs of chromosomes line up together at the middle of the cellChromosome centromeres attach to spindle fibers.

Anaphase I homologous chromosomes separate & move to opposite ends (centromeres do not split)

Telophase I & Cytokinesis spindle disappears and the cell divides

Meiosis I results in 2 haploid(1N) daughter cells, each with half the number of chromosomes as the original cell.

Meiosis II

During the second meiotic division, doubled chromosomes will be separated much like they were in mitosis.

Prophase IIProphase II

the spindle apparatus forms and the chromosomes condense

Metaphase II

a haploid number of chromosomes line up at the equator (middle)

Anaphase II

sister chromatids are pulled apart at the centromere & move to opposite poles

Telophase II (includes cytokinesis)

chromosomes reach the poles and the nuclear membrane and nuclei reform

4 new daughter cells are produced

each new daughter cell has the haploid number of chromosomes

Differences: Differences: In females: In females: 1 mature egg, 3 polar 1 mature egg, 3 polar

bodies which break downbodies which break down Women born with all eggs Women born with all eggs

they will have, meiosis I they will have, meiosis I occurs before birth, meiosis occurs before birth, meiosis II occurs once a month II occurs once a month

Much larger (egg)Much larger (egg) Have all X chromosomesHave all X chromosomes Has no method of Has no method of

movement movement Occurs in ovariesOccurs in ovaries oogenesisoogenesis

In males:In males: 4 mature sperm4 mature sperm Males begin to produce Males begin to produce

sperm after puberty, sperm after puberty, produced constantly until produced constantly until death; meiosis II occurs death; meiosis II occurs immediately after meiosis Iimmediately after meiosis I

Much smaller than eggMuch smaller than egg May have X or Y May have X or Y

chromosomeschromosomes Have flagella to moveHave flagella to move Occurs in testesOccurs in testes spermatogenesisspermatogenesis

Meiosis/gamete productionMeiosis/gamete production

Females have XX for last pair of Females have XX for last pair of chromosomeschromosomes

Males have XY for last pairMales have XY for last pairSince all eggs are X, father Since all eggs are X, father

determines the sex of the child since determines the sex of the child since the sperm may be X or Ythe sperm may be X or Y